Hey Chris! Welcome to the community 
Thanks for posting your question here! It looks like this error message has to do with how Coda handles arrays in image columns. For example, in the screenshot below, that first row containing two images is being evaluated as two separate lists containing images**. And image file columns don’t support multiple lists, hence the error.
I’ll be sure to file a bug report for this issue, since there’s likely a better way we can handle this.
In the meantime, you could remove the error message by either changing the column type from image to text, or by adding .ListCombine()
to the end of the formula for the column.